That Neuroscience Guy - The Neuroscience of Fear

Episode Date: December 2, 2021

Humans both love and hate fear. Whether it's hiding under the covers during a scary movie or jumping out of a plane headfirst, we all experience fear.  In today's episode of That Neuroscience Guy, we discuss how our brains process fear and how it affects our behaviour. 

Hi, my name is Olof Kregolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. We've all experienced fear. For some of us, it's a part of our daily lives. We live with it every single day. And for others, it's something that we seek out. We want that sensation and it makes us happy in a sense. And for most of us, it's something we experience from time to time. It's just another emotion that we have to live with and process. On today's podcast, the neuroscience of fear. But first, I just want to quickly say sorry. We're a little bit late this week. We normally release on Sundays, and today it's Wednesday, and I'm recording at three in the

afternoon. My apologies. I was a little bit under the weather, but I'm feeling better today. Not COVID, just a common cold. Anyway, sorry for being a bit late. We'll be on time this week and moving ahead. The origins of fear from an evolutionary perspective stem back to the fight or flight response. At a very primitive low level, this response is an emotional response that signals danger. We need to either stand and fight or we need to run away. So at the lowest levels, we share fear with a lot of other animals. If you recall in season one, we talked a bit about emotion and specifically the role of the parasympathetic and the sympathetic nervous system. If you remember, these two systems work together. For instance, one increases our

heart rate and the other decreases our heart rate. So these are the mechanisms that give us those responses when we're afraid. Our heart rate might speed up, our breathing picks up, and we sweat a little bit more. All of the physical responses that we fear. And with that increase in heart rate that I mentioned, blood pressure rises, blood flow, and the stream of glucose to our skeletal muscle increases. The brain becomes hyper alert. Our pupils dilate, the bronchi dilate, organs not vital in survival, such as the gastrointestinal system, they begin to shut down. Our body's preparing for actions. Now that's the low-level fear response. In terms of brain structures, the story of fear comes to some

other midbrain structures and the cerebral cortex. If you think back to season one in our podcast on emotion, you'll remember the hypothalamus. The one way I always talk about the hypothalamus is that it's a regulatory structure. If you recall, it's located in the midbrain near the brainstem. And the hypothalamus, one of its main jobs is to help control the parasympathetic and sympathetic nervous system. It tells these systems what to do when we're experiencing fear. Now, it's important to realize that not a lot of high-level processing goes on in the hypothalamus. It's like I said, it's a regulatory structure. So it controls these lower-level systems,

speed up the heart rate, and it's turned on by other parts of the brain, the parts of the brain that truly create the fear response for us. on by other parts of the brain, the parts of the brain that truly create the fear response for us. Now, it's important to realize that fear is a learned response. This is why very young children might blindly wander into a dangerous situation, and they're not able to process that they should be afraid. In fact, I used to joke with my classes, I still do, that you could imagine training a whole generation of young children that when they hear that scary music in horror movies, you'll have to forgive me, but you know that, but that doesn't predict a monster leaping out or a shark swimming through

the water or someone's head rotating around and around. It leads to a happy outcome. I always visualize Care Bears dancing. And what would happen is children would learn that, yep, that music is actually a good thing. Please don't do this to your children. They're going to get a lot of bad surprises if you do. So a lot of how our brain processes fear is by context. This is why we have a fear response. And sometimes in other people think it's exciting. You know, take a roller coaster. Some of us are scared of roller coasters. I have to admit, I can tweak a bit myself. So when I get on that ride, I'm a little bit scared, but some of us aren't. This is awesome. Like I want to do this. So basically that comes down to some individual

differences, but it's context. And that context, one way to think of it is experience. So one way to think about this is that there is a tug of war going on in your brain when you're processing fear responses. You've got another brain structure you might remember, the amygdala, and it's providing this emotional edge to things. It's going, oh, this is not good. But you've also got your prefrontal cortex, and that part of the brain is going, well, hang on, let's just assess the situation and see where we're at. So when that analytical system, the prefrontal cortex, gives feedback to the emotional brain,

it basically says, hey, we're okay. This isn't a bad space. Then you can shift away from that high arousal state associated with fear and go into one of enjoyment or excitement. You know, think about going to the haunted house during Halloween. I'm sure it a lot today, but that's another thing I never really enjoyed. But some people love it. They love the ghoul jumping out at you, but they know it's not really a threat. So you quickly relabel that experience and you just go, oh, that was exciting. All right. But you could imagine if you were walking in a dark alleyway one night and someone jumped out and scared you, you'd probably process that a lot differently. And this is what I meant by

context, because both your emotional brain and your analytical brain would be in agreement and saying, hey, this isn't good. It's time to do something. And of course, what they would do is they would reach out to the hypothalamus and they would say, all right, time to do some responses that are associated with being afraid. Now, like I said, this starts with the amygdala. We'll come back to the prefrontal cortex. But if you recall, the big thing the amygdala does is give things emotional salience. Now, emotional salience, I've talked about it before, but essentially it's a value. It's how emotional something is to you. And an example that I also like is you can imagine that you

might have an old sweater that's your favorite sweater, and it has a high emotional salience to you because it's associated with some good memories. But to another person, that same sweater might have no emotional salience. So the amygdala, when you're in these frightening situations, is the part of the brain responding with the emotional response. So you see something that's scary and the amygdala is giving it a whole bunch of emotional salience, so you start getting scared. And of course, like I mentioned just a few minutes ago, that triggers the hypothalamus and the sympathetic and parasympathetic nervous system. So like I said, our hearts beat faster, we breathe more heavily, and we sweat a bit more.

The amygdala is doing other things too, though, which is part of the fear response. It starts releasing stress hormones. Remember, hormones are those chemicals in the bloodstream that are a part of the fear response, and they're part of what helps you or makes you feel afraid. In fact, when you're scared, the amygdala even activates the motor system. It's getting it ready for action. The fight-or-flight response, literally. And that's why if you scare someone, they might lash at you very suddenly. All right. And that's because their motor system is jacked up and it's ready for action. Now, part of what makes the fear response, the fear response is the amygdala

is directly connected to the hippocampus. And if you remember, the hippocampus is involved in memory. So when you're processing this situation, one of the other things that kicks in very early on is this memory response, all right? Again, interpreting context. The hippocampus is going, what is this? Is this a real threat or is this a perceived threat? So for instance, if you see

a lion in the wild, you might be terrified because of context. There's nothing between you and the lion. It's the wild and you're going, what's going on? Where I live on Vancouver Island, this can happen with bears quite literally. However, if you saw a lion or a bear in a zoo, you know, you might get more of a curiosity reaction because the hippocampus is giving you information. And it's basically saying, hey, this isn't that bad. We're safe here. And literally, the inhibitory pathways in the brain dampen the amygdala's fear response and turn it down and basically says, okay, we don't need to be afraid right now. And this, of course, like I said and mentioned a few times, also

involves the prefrontal cortex. It's sitting there providing that high-level analysis of, are things really okay? So memory plays a role. Now, I've talked about an example just now where memory is a positive in a sense. It's saying, okay, it's a zoo, we're okay. But you can also imagine memory hindering us. So imagine you've been attacked by a particularly aggressive dog, all right, or you've even just seen that happen. That memory might dial up the fear response. So as opposed to dampening the amygdala, what's happening is the hypothalamus is saying, okay, no, no, this is really bad. We need to respond here. And another thing that's interesting is we as humans can also process information. So a sign that says beware of dog might also trigger a fear response,

even if you don't actually see the dog. Or one that I personally relate to, again, is that seatbelt sign. When it comes on in the middle of a flight, I always interpret that as meaning this isn't going to be good. Now interestingly as humans we're also really social creatures so our fear can be transmitted. The amygdala, the hypothalamus and the prefrontal cortex can be activated by other people. You might see someone responding and it's clear they're getting afraid and that triggers your amygdala to respond, especially if you're unsure of the context. And this works again in a supportive fashion. You might see a friend respond and

they're clearly not scared, so it calms you down. We're dampening the amygdala's response. you down. We're dampening the amygdala's response. So to emphasize this, this is this tug of war. You've got the amygdala adding this emotional salience to things that is the fear response, and you've got the prefrontal cortex in your memory system, the hippocampus. The hippocampus is recalling what you know about this to add the context, and the prefrontal cortex is doing yet logical evaluation. Shouldn't we be afraid, or should we be? In fact, this is one of the things that might be a source of individual differences for us. Someone that we know might be perceiving a situation as, yeah, this is okay, but for us, it's just a bit too real and we get really, really scared. And this is what happens in horror movies as an example. For some of us, Chucky the doll

might be really real and we get really, really scared. But for other people, they just go, yeah, I've seen this before. It's a bit of a joke. But interestingly, the same person might be terrified by the exorcist because that for them feels too real. And the fear response is not modulated by the cortical brain. The amygdala is running wild. You know, this also extends to the logical brain basically controlling things too much. You could imagine watching a scary movie and you're over-processing it and your brain's going, well, this isn't real. This isn't real. That's not possible. There's no such thing as zombies. And that might be why that person won't even enjoy the show because they're completely

shutting down that emotional response. Now, it's important to note that abnormal levels of fear and anxiety aren't good. All right. So if you do have anxiety disorders or you're constantly in fear, this is something that you probably should talk to someone about because these things can change your life. If you're constantly in a state of fear, these can have chronic and debilitating circumstances to them. They can really be bad. So I'm not going to get a lot into that, but if people are interested, email the show and we can cover that on another week's episode. So as we wrap up here, what's fear and what's the neuroscience of fear? Well, at the high level, it's the emotional response to the amygdala

saying we should be afraid. And this is tied to context. The hippocampus processing the situation you're in and going, yep, this isn't a good situation or yes, this is. And then the logical brain and that tug of war basically saying, okay, we're safe here.

We don't need to be afraid or no, actually, this is pretty bad. We should be. And if that happens and you evaluate that you should be afraid, well, then you trigger those low level systems through the hypothalamus and you have a fear response. Or if you evaluate that you're okay, then the net result of the prefrontal cortex's engagement is to dampen the emotional response. So you're not afraid. All right. That's all I have to say about the neuroscience of fear. Sorry one more time again for releasing a little bit late.

Like I said, had a bit of a cold, but luckily I'm over it now. Remember, please follow me on Twitter. It really helps, That Neurosci Guy. And we do post some videos on our YouTube channel, That Neuroscience Guy. And, of course, subscribe and listen to the podcast. My name is Olive Kregolson, and I'm That Neuroscience Guy. Thanks for listening and see you next week.